Field of the Disclosure
The present disclosure generally relates to a centralizer.
Description of the Related Art
A wellbore is formed to access hydrocarbon bearing formations, such as crude oil and/or natural gas, by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive or rotary table on a surface platform or rig, and/or by a downhole motor mounted towards the lower end of the drill string. After drilling to a predetermined depth, the drill string and drill bit are removed and a casing string is lowered into the wellbore. An annulus is formed between the string of casing and the wellbore. The casing string is cemented into the wellbore by circulating cement slurry into the annulus. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain formations behind the casing for the production of hydrocarbons.
Centralizers are mounted on the casing string to center the casing string in the wellbore and obtain a uniform thickness cement sheath around the casing string. Each centralizer has blades extending out from the casing wall and contacting the wellbore, thereby holding the casing string off of direct contact with the wellbore wall, and substantially centralizing the casing therein. To accomplish that goal, the centralizer blades typically form a total centralizer diameter roughly the diameter of the wellbore in which the casing string is run.
One type of centralizer is rigid including a solid central tubular body having a plurality of solid blades integral with the central body, the blades extending out to the desired diameter. Another type is a bow spring centralizer, which includes a pair of spaced-apart bands locked into place on the casing; and a number of outwardly bowed, resilient bow spring blades connecting the two bands and spaced around the circumference of the bands. The bow spring centralizers are capable of at least partially collapsing as the casing string is run into the wellbore to pass through any restricted diameter location, such as a piece of equipment having an inner diameter smaller than the at-rest bow spring diameter, then spring back out after passage through the reduced diameter equipment.